The present invention relates to a solid electrolytic capacitor for use in an electronic circuit in an electronic device.
As electronic devices handles higher frequencies according to development of digital technology, a high-frequency capacitor having a small size, a large capacitance, a small internal impedance at high frequencies is demanded. To have the internal impedance reduced, a solid electrolytic capacitor are focused to have a small equivalent serial resistance (ESR) as well as a small equivalent serial inductance (ESL) at high frequencies.
FIG. 11 illustrates a conventional solid electrolytic capacitor 301. A porous valve metal film 201 is formed by etching a valve metal film made of valve metal, such as aluminum. A dielectric layer 202 is formed on the porous valve metal film 201. An insulating isolator layer 209 for separating between a lead portion of the porous valve metal film 201 and a solid electrolyte layer 206 is formed on the dielectric layer 202. The solid electrolyte layer 206 is provided on the dielectric layer 202. A carbon layer 207 is provided on the solid electrolyte layer 206, and a silver paste layer 208 is formed on the carbon layer 207, thus providing a capacitor element. The carbon layer 207 and the silver paste layer 208 functions as a collector. A desired number of such capacitor elements are stacked with silver paste. The silver paste layer 208 of each capacitor element is joined to a negative electrode lead frame 211 with the silver paste while the lead portion of the porous valve metal film 201 is joined to a positive electrode lead frame 212 by welding or the like. The stacked capacitor elements are then encapsulated by molding in a resin package 210.
FIG. 12 illustrates another conventional solid electrolytic capacitor 302. A dielectric layer 223 is formed on a porous valve metal body 222. One end of a valve metal lead 221 made of tantalum or niobium is embedded in the body 222. An insulating isolator layer 227 is provided between the valve metal lead 221 and the dielectric layer 223. A solid electrolyte layer 224 made of electrically conductive polymer is formed on the dielectric layer 223. A collector consisting of a carbon layer 225 and a silver paste layer 226 is formed on the solid electrolyte layer 224. The silver paste layer 226 is joined to a negative electrode lead frame 229 by the silver paste while the valve metal lead 221 is joined to a positive electrode lead frame 230 by welding. The stacked capacitors are then encapsulated by molding in a resin package.
The conventional solid electrolytic capacitor 301 with the positive electrode made of aluminum has an ESR smaller than that of the conventional solid electrolytic capacitor 302 with the positive electrode made of tantalum, but has a capacitance smaller than that of the capacitor 302. The conventional solid electrolytic capacitor 302 with the positive electrode made of tantalum has a large capacitance but has a large ESR.
A first capacitor element includes a porous valve metal film, a first dielectric layer provided on the porous valve metal film, a first solid electrolyte layer provided on the first dielectric layer, and a first collector layer provided on the first solid electrolyte layer.
A second capacitor element includes a valve metal film, a porous valve metal body provided on the valve metal film, a second dielectric layer provided on the porous valve metal body, a second solid electrolyte layer provided on the second dielectric layer, and a second collector layer provided on the second solid electrolyte layer.
A solid electrolytic capacitor includes a stacked-assembly including the first capacitor element and the second capacitor element stacked, a package for encapsulating the stacked-assembly, a first external electrode connected to the porous valve metal film and the valve metal film, and a second external electrode connected to the first and second collector layers. At least a portion of the first external electrode is provided on a first side of the package. At least a portion of the second external electrode is provided on a second side of the package.
The capacitor has a small size and a large capacitance while having a small equivalent serial resistance and a small equivalent serial inductance.